The objective of this research is to study mutagenesis at the DNA level in mammals and to evaluate genetic and biochemical events in certain mutants as models of human genetic diseases. A major problem in mutagenesis is that the level and specificity of response is very different between indicator organisms; predictions about induced mutagenesis may not be relevant. Significant variation is due to the diversity of the marker genes; a single sequence needs to be used among various organisms and tissues. Our analyses are based on reverse mutations among single copies of the phi X174 virus as a shuttle vector in different species. The accomplishments are as follows. 1) Experiments with transgenic cell cultures and phi X174am3cs7O indicate that the approach is sensitive enough to study mutations among single copies of the vector DNA recovered from the host. 2) Transgenic inbred C57B1/6 mice containing the phi X vector have been produced and the transgene has been transmitted to offspring. Each hemizygous founder contains more than 50 copies per genome. Mating schemes have expanded the number of copies per genome and produced mice homozygous for the vector at each allelic insertion site. 3) Methods have been developed to efficiently recover the vector from the transgenic mice and measurements of mutation rates are in progress. 4) A second type of transgenic phi X vector with a different mutation site and reversion mechanism has been developed. Production of transgenic mice with this new vector is in progress. The use of integrated transgenic vector can combine a theoretical study of mutations in several model organisms with the assessment of mutagenic hazard. A single DNA sequence can be exposed and analyzed as naked DNA, as a single stranded virus, double stranded in bacteria, and in the nuclear genome of mammalian cells or transgenic mice. In addition, such an approach may allow us to examine in vivo mutagenesis and repair in many somatic tissues and in gametogenic tissue during development or as a function of aging and various conditions of environmental exposure.